The invention relates to a dematrixing circuit of the switched-capacitor type for dual channel TV stereo sound signals, comprising first and second signal inputs for applying a stereo sum signal ##EQU2## thereto and one of the two left and right stereo signals (for example, R), the amplitude of the latter stereo signal being twice as large as that of each of the two stereo signals in the stereo sum signal, and comprising first and second signal outputs for supplying the dematrixed stereo signals.
A dematrixing circuit of this type is known from the article "Switched capacitor stereo decoder for TV and radio receivers" by A. H. M. van Roermund et al, published in IEEE Transactions on Consumer Electronics, Vol. CE-31, No. 3, August 1985, pages 461-468.
Said article describes the dematrixing circuit as part of a decoder for two TV sound signals, which may comprise stereo information or mutually independent sound information. The nature of this information is indicated by means of a signal frequency (117.5 Hz or 274.1 Hz) being AM modulated on a pilot in the channel of one of the two TV sound signals. This signal frequency is detected by means of a pilot identification circuit and used as a control signal for a selection circuit which is coupled to the output of the dematrixing circuit.
In the case of reception of TV stereo sound signals a transfer with a possible amplitude adaptation and de-emphasis of the left or right stereo signal (for example, R) applied to the second signal input is effected in the dematrixing circuit to one (for example, the said second) of the two signal outputs. The other stereo signal (in this case L) is dematrixed therein by a suitable combined processing of the signals ##EQU3## and (R) applied to the two signal inputs, and is, eventually after a possible amplitude adaptation and de-emphasis, applied to the other (for example, the first) signal output. After passing through said selection circuit these two dematrixed TV left and right stereo sound signals become available at the outputs of the decoder for further audio signal processing or reproduction.